Fungibility ... means the object in reference can't just randomly transform from an elephant to a flamingo.
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Fungibility is simply the property that any unit of some substance is functionally equivalent to all other units of that substance.
Don't play stupid. You know damn well bitcoin is not fungible
Not perfectly fungible, no. Can you name anything that is? Other than XMR and relatives, and ZEC and relatives, nothing comes close. Certainly neither PMs nor fiat.
Bitcoin Segwit is certainly at least a two-set system as far as fungibility goes. Bitcoin Cash is much better on the fungibility scale. It at least is not a two-set system.
nor money by definition
Incorrect. Your repeated assertions of this have been supported by insufficient evidence.
, and that an "evolving protocol" is also never going to be fungible
To the extent that the units are indistinguishable from each other, they are perfectly fungible. Yes, as long as there is a way to distinguish, then they are to some degree infungible. And to be pedantic, any measure of infungibility means 'not fungible' (again, what is?). But the protocol change has absolutely nothing to do with this. When the protocol changes, all the units change in the exact same manner.